This paper presents an atomic-scale study of contact, indentation, and
subsequent pulling and dry sliding of a sharp and blunt metal tip on
a metal surface. The evolution of atomic structure and the variation o
f perpendicular and lateral forces are calculated by molecular-dynamic
s methods using an empirical potential based on the embedded-atom mode
l. The sharp tip experiences multiple jumps to contact in the attracti
ve force range. The contact interface grows discontinuously mainly due
to disorder-order transformation leading to disappearance of a layer
and hence abrupt changes in the normal-force variation. Atom exchange
occurs in the repulsive range. During the pulling off, the connective
neck is reduced discontinuously; however, not all the abrupt changes o
f the pulling force are associated with the creation of a new layer in
the neck. The sliding of the sharp tip (or single asperity) induces t
wo consecutive structural transformations that occur periodically, but
end with the wear of a layer. The situation for a blunt tip is, howev
er, quite different.